October’s Opals and Tourmalines Part I

Oh! October. The birthstones for October are opal and pink tourmaline. Let’s start with Opals!

Opals are an unusual mineral type in that they are up to 30 percent water! The chemical description is SiO2 ยท nH2O where n is often given as 1.5. There is some controversy as to whether or not opal should be considered a true mineral species, but because of its long history no one has yet (as far as I know) changed that designation. It is, however, actually a combination of various amounts of two minerals, Cristobalite and/or Tridymite. When tiny silica spheres (amorphous form of silica) is in the mix, the result is a sort of diffraction grating which refracts light and gives us the gemstone variety of opal.

The name, opal derives from Sanskrit, upala, meaning “precious stone,” and it was well known to the ancient Greeks and Romans as well. It is a rather fragile gem because of the water content, needing to be protected from drying out in heat and from harsh chemicals both of which will cause the loss of the “play of light.” Red opal is also called Fire Opal while green opal is called Prase. Opals also come in a milky white (when tansluscent this is “opalescence”), yellow, and black. Specimens have been found on every continents – including Antarctica.


Black Opal image at opal33.com

An Opal example from Opal33.com

Pink Tourmaline is the alternate birthstone for October but it is by no means a lesser choice as we shall see next week.

4 Responses to “October’s Opals and Tourmalines Part I”

  1. Marsha Says:

    I love your posts! Always something I don’t know.

  2. Triz Designs Says:

    I love opals and this is a great and informative post!!

  3. Olga Says:

    That was a very interesting reading! Thanks!

  4. Patricia C Says:

    Thank you Marsha, Triz, and Olga. I am enjoying doing this monthly series as I learn a few things from it myself.